A fundamental fact of vision is that our perception of the external world is shaped by a number of behavioral and contextual factors. These factors include visual selective attention, in which sensory information is filtered in favor of items that are behaviorally and contextually relevant. It also includes the modulation of sensory signals by diffusely projecting neuromodulatory systems, and it includes the modulation of visual processing during saccadic eye movements which occur several times each second. The current proposal focuses on addressing key, complementary questions about the neural mechanisms underlying these basic factors that influence visual processing within the primate brain. Evidence to date has established that brain structures involved in gaze control, such as the frontal eye field (FEF) in prefrontal cortex (PFC), are causally involved in modulating visual signals within posterior visual cortex, and that such structures play a role in each of the above forms of sensory modulation. In the first aim, we will test the dependence of spatial attention and attentional modulation on the FEF, and identify the functional properties of FEF feedback projections to visual cortex. Although it has become clear that the FEF plays a causal role in visual spatial attention and the correlates of attention in visual cortex, this evidence is incomplete. In particular, it is not known if the modulation of activity within posterior visual cotex that accompanies selective visual attention actually depends on the FEF. We will address this crucial question by testing the impact of local inactivation of the FEF on visual spatial attention and its corresponding neural correlates within area V4 of monkeys using multi- electrode, laminar recordings. In addition, we will determine the functional class(es) of FEF neurons that project directly to area V4. In the second aim, we will determine the influence of catecholamines on the control of spatial attention and attentional modulation by the FEF. Studies conducted in rodents and primates suggest that both noradrenaline and dopamine play a role in the prefrontal control of cognitive functions such as attention and working memory. We will establish, or rule out, a role of these neuromodulators in the control of visual selective attention, and correspondingly the modulation of visual cortical activity during attention, by the FEF. In the thid aim, we will identify neural correlates of presaccadic changes in visual processing and probe their source. Saccadic eye movements lead to frequent and substantial displacements of the retinal image, yet they go unnoticed. The basic question of how the visual and oculomotor systems combat the problem of frequent disruptions in the visual image remains unsolved, but evidence suggests the existence of robust changes in visual representations at some stages in the visual system just prior to saccade onset. We will measure the dynamics of visual receptive fields of FEF and area LIP neurons, we will test whether neurons in the FEF and LIP exhibit saccadic suppression, and we will test the hypothesis that saccadic suppression of visual cortical contrast sensitivity is driven at least in part by the FEF. Overall, our focus on the more significant factors affecting visual processing, combined with our use of state-of-the-art neurophysiological approaches and causal methods, are likely to produce results that exert a large and sustained impact on our understanding of the neural mechanisms of visual perception.